Water-slidable/oil-slidable film, production method thereof, and articles having the surface coated therewith

ABSTRACT

The problem to be solved by the present invention is to provide a water-slidable/oil-slidable film that is easily producible and has improved durability. 
     A water-slidable/oil-slidable film of the present invention comprises: a porous polymer film having a three-dimensional entangled network structure of a fibrous polymer and a continuous pore structure as the empty space of the network structure, and a slippery liquid infused in the pores of the porous polymer film.

RELATED APPLICATIONS

This application claims the priority of Japanese Patent Application No.2014-133786 filed on Jun. 30, 2014, which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to the provision of awater-slidable/oil-slidable film that can be easily produced and exertan excellent antifouling effect and the improvement of its durability.The invention further relates to the provision of awater-slidable/oil-slidable film having high transparency and sufficientstrength as a self-standing film.

BACKGROUND OF THE INVENTION

The development of antifouling surfaces has been desired in numerousfields such as solar cells, automobiles, medical devices, fueltransportation, construction, and food containers. In recent years,slippery liquid-infused porous surfaces (SLIPS) have been reported asthe new type of antifouling surface. These are low-energy poroussurfaces wherein liquid lubricant is infused (refer to Non-PatentLiterature 1). SLIPS exhibit non-wetting properties against most fluidsand are stable at a high temperature and a high pressure because thelubricant is inside the pores. For example, non-wetting surfaces basedon the lotus leaf effect have been studied over several decades.However, it has been very difficult to obtain an antifouling surfaceagainst a low-surface-tension liquid and a surface stable against dropimpact, ultra-high temperature, or ultra-high pressure. Thus, SLIPS area very appealing material.

There are numerous reports concerning the production method of SLIPS;however, they have not been versatile enough because of the followingreasons. Won et al. have used a poly(tetrafluoroethylene) mesh and anepoxy resin array as the rough surface for lubricant application (referto Non-Patent Literature 1). The moldability of a PTFE mesh is verypoor; therefore, it cannot be applied to the surface of a complexstructure, and it is not transparent in the visible light region. On theother hand, the surface of an epoxy resin array can be formed into acomplex structure; however, the two-step soft-lithography process takesa long time. These production processes are not suitable for massproduction and they are not versatile.

In addition to these, a photolithography method, deep reactive ionetching method, chemical vapor deposition, etc. can be listed ascumbersome, time-consuming, high-cost processes. On the other hand, Maet al. reported a production process of SLIPS by alumina sol-gel as alower-cost simpler method in the formation of a rough surface (refer toNon-Patent Literature 2). This is a simple wet process, and a layerhaving a high transmittance in the visible light region can be obtained.However, annealing at a high temperature of about 400° C. and thereduction of the surface energy are necessary; thus the selection ofsubstrates is limited. In addition, the additional processes andmaterials are necessary; thus the cost will increase. The preparationmethods such as boehmite treatment of aluminum, alkaline etching ofcopper, and electrolytic polymerization of polypyrrole also have similarissues.

Among the substrates used as the rough porous surface in theconventional SLIPS, the epoxy resin array by a photolithography methodand porous silicon by etching have fine needle-like asperity ornon-continuous fine through-holes (lotus root-type through-holes) formedon the surface. An alumina thin film formed by a sol-gel method merelyhas fine asperity on the surface. Therefore, liquid lubricant infused onthese rough porous surfaces, of the SLIPS, relatively easily seeps outor leaks out, and the liquid lubricant must frequently be replenishedduring use.

A porous PTFE sheet formed by a stretching method has a more complexpore structure; however, it is a uniaxially-stretched windowblind-shaped sheet or a biaxially-stretched cobweb-shaped sheet. Thus,liquid lubricant cannot be retained inside the pores over a long period,and in particular, the tolerance to vibration and pressure has not beensatisfactory.

Furthermore, the development of a transparent film that can provide anantifouling effect by pasting on the products such as window glass andautomobile windshield, which require transparency, is considered to bevery useful. However, the surface of the article is directly treated inthe case of SLIPS by photolithography, etching, or sol-gel method, and aself-standing film is not formed. On the other hand, a porous PTFE sheetby the stretching method can be a self-standing film; however, thetransparency is poor because the film is relatively thick. Thus, therehas been no conventional SLIPS having high transparency as well as thesufficient strength as a self-standing film.

CITATION LIST Non-Patent Literature

-   Non-Patent Literature 1: Wong, T.-S.; Kang, S. H.; Tang, S. K. Y.;    Smythe, E. J.; Hatton, B. D.; Grinthal, A.; Aizenberg, J. Nature    2011, 477, 443-447.-   Non-Patent Literature 2: Ma, W.; Higaki, Y.; Otsuka, H.;    Takahara, A. Chem. Commun. 2013, 49, 597-599.

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

The problem to be solved by the present invention is to provide awater-slidable/oil-slidable film that is easily producible and hasimproved durability and to provide a production method thereof. Inaddition, it is to provide a water-slidable/oil-slidable film havinghigh transparency as well as sufficient strength as a self-standingfilm.

Means to Solve the Problem

The present inventors have diligently studied to solve the aboveproblem. As a result, the present inventors have found that awater-slidable/oil-slidable film that exhibits an excellent antifoulingeffect can easily be produced by mixing with stirring a polymer and apore-forming agent, at a specific ratio, in a volatile organic solvent,applying it on the substrate and drying, removing the pore-forming agentwith an organic solvent to obtain a porous polymer film, and infusing aslippery liquid to this porous polymer film. The present inventors havealso found that the durability of the obtainedwater-slidable/oil-slidable film is also excellent. Furthermore, thepresent inventors have found that a water-slidable/oil-slidable filmhaving high transparency and having sufficient strength as aself-standing film can be obtained by this method, thus leading to thecompletion of the present invention.

That is, the water-slidable/oil-slidable film of the present inventionis characterized by comprising: a porous polymer film having athree-dimensional entangled network structure of a fibrous polymer and acontinuous pore structure as the empty space of the network structure,and a slippery liquid infused in the pores of the porous polymer film.

In addition, in the water-slidable/oil-slidable film, it is preferablethat the average pore diameter of the porous polymer film is 500 to 1000nm. In addition, it is preferable that the average fiber diameter of theporous polymer film is 100 to 400 nm. In addition, it is preferable thatthe root-mean-square roughness of the porous polymer film is 0.3 to 0.6μm.

In addition, it is preferable in the water-slidable/oil-slidable filmthat the porous polymer film is made of a fluorine-based resin or asilicone resin. Furthermore, it is preferable that the porous polymerfilm is made of polyvinylidene fluoride or copolymers thereof.

In addition, it is preferable that the slippery liquid has affinity tothe porous polymer film in the water-slidable/oil-slidable film. Inaddition, it is preferable that the slippery liquid is a fluorine-basedoil or silicone oil. Furthermore, it is preferable that the slipperyliquid is perfluoropolyether.

In addition, it is preferable that the refractive index differencebetween the porous polymer film and the slippery liquid is 0.3 or lessin the water-slidable/oil-slidable film. In addition, it is preferablethat the average transmittance of the light with the wavelength of 400to 700 nm is 80% or higher in the water-slidable/oil-slidable film.

The production method of the water-slidable/oil-slidable film of thepresent invention is characterized by comprising:

a step of mixing and stirring a polymer and a pore-forming agent thatdoes not dissolve the polymer with a volatile organic solvent that candissolve both the polymer and the pore-forming agent,

a step of forming a coating film by applying the mixture obtained in thepreceding step on the surface of an article, and vaporizing the volatileorganic solvent,

a step of forming a porous polymer film by contacting the coating filmobtained in the preceding step with an organic solvent allowing that candissolve the pore-forming agent without dissolving the polymer, toremove the pore-forming agent,

a step of infusing a slippery liquid inside the pores of the porouspolymer film obtained in the preceding step.

In the production method of the water-slidable/oil-slidable film, it ispreferable that the mixing ratio (mass ratio) of the polymer to thepore-forming agent is 1:1.5 to 1:5.

In addition, it is preferable that the polymer is a fluorine-based resinor silicone resin in the production method of thewater-slidable/oil-slidable film. Furthermore, it is preferable that thepolymer is polyvinylidene fluoride or copolymers thereof. In addition,it is preferable that the polymer is soluble in acetone and insoluble inethanol in the production method of the water-slidable/oil-slidablefilm.

In addition, it is preferable that the pore-forming agent is anethanol-soluble low-molecular-weight solvent in the production method ofthe water-slidable/oil-slidable film. Furthermore, it is preferable thatthe pore-forming agent is phthalic acid or derivatives thereof.

In addition, it is preferable that the volatile organic solvent is anorganic solvent with a boiling point of 100° C. or lower in theproduction method of the water-slidable/oil-slidable film. Furthermore,it is preferable that the volatile organic solvent is acetone.

In addition, it is preferable that the organic solvent that can dissolvethe pore-forming agent without dissolving the polymer is ethanol in theproduction method of the water-slidable/oil-slidable film.

In addition, it is preferable that the slippery liquid is afluorine-based oil or silicone oil in the production method of thewater-slidable/oil-slidable film. Furthermore, it is preferable that theslippery liquid is perfluoropolyether.

The article of the present invention is characterized by having thesurface coated with the water-slidable/oil-slidable film.

Effect of the Invention

According to the present invention, a water-slidable/oil-slidable filmthat can be easily produced and has an excellent antifouling effect canbe obtained, and its durability is also excellent. In addition, awater-slidable/oil-slidable film having high transparency and sufficientstrength as a self-standing film can be obtained by the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the cross section for thewater-slidable/oil-slidable film of the present invention.

FIG. 2 is a schematic illustration of the production method of thewater-slidable/oil-slidable film as one example of the presentinvention.

FIG. 3A is an SEM photograph of a PVD-HFP porous polymer film preparedin the polymer/pore-forming agent (PVDF-HFP/DBP) ratio=1:0.5.

FIG. 3B is an SEM photograph of a PVD-HFP porous polymer film preparedin the polymer/pore-forming agent (PVDF-HFP/DBP) ratio=1:1.

FIG. 3C is an SEM photograph of a PVD-HFP porous polymer film preparedin the polymer/pore-forming agent (PVDF-HFP/DBP) ratio=1:2.

FIG. 3D is an SEM photograph of a PVD-HFP porous polymer film preparedin the polymer/pore-forming agent (PVDF-HFP/DBP) ratio=1:5.

FIG. 4 shows the measurement results of the pore size and fiber diameterfor various PVD-HFP porous polymer films.

FIG. 5 shows the measurement results of the surface roughness(root-mean-square roughness) for various PVD-HFP porous polymer films.

FIG. 6 shows the measurement results of the thickness for variousPVD-HFP porous polymer films.

FIG. 7 shows the measurement results of the sliding angles for water andoleic acid on various PFPE-infused PVD-HFP porous polymer films.

FIG. 8 shows explanatory illustrations of liquid adhesion on the surfaceof a PVDF-HFP porous (PFPE-infused) film.

FIG. 9 shows the measurement results of the transmittance, in thevisible light region, for various PVDF-HFP films before and after theinfusion of PFPE.

FIG. 10 shows the measurement results of the transmittance at thewavelength of 600 nm for various PVDF-HFP films before and after theinfusion of PFPE.

FIG. 11 is a photograph of glasses whose lens surface is coated with thePVDF-HFP porous (PFPE-infused) film (left lens: uncoated; right lens:film-coated).

FIG. 12 shows photocurrent density (Jsc)-voltage (Voc) curves for a baresolar cell, a glass-covered solar cell, a solar cell covered withPVDF-HFP film (before PFPE infusion), and a solar cell covered withPVDF-HFP film (after PFPE infusion).

FIG. 13 shows the measurement results of the tensile strength for thePVDF-HFP (PFPE-infused) self-standing film.

FIG. 14 shows measurement results of the extension rate for the PVDF-HFP(PFPE-infused) self-standing film.

FIG. 15 is a photograph of the PVDF-HFP (PFPE-infused) self-standingfilm.

FIG. 16 shows the measurement results of the water sliding angle for thePVDF-HFP (PFPE-infused) film after spinning at various spin speeds for 1minute.

FIG. 17 shows the measurement results of the water sliding angle for thePVDF-HFP (PFPE-infused) film after applying abrasion under the loadingcondition of 80 g/cm² for the stated time.

FIG. 18A is a photograph of the PVDF-HFP (PFPE-infused) film when bloodwas dropped thereon.

FIG. 18B is a photograph of the PVDF-HFP (PFPE-infused) film when ahigh-viscosity drink (sweet bean soup) was dropped thereon.

FIG. 18C is a photograph of the PVDF-HFP (PFPE-infused) film when foodoil was dropped thereon.

FIG. 18D is a photograph of the PVDF-HFP (PFPE-infused) film whencleaner was dropped thereon.

DESCRIPTION OF REFERENCE NUMBERS

-   10 Water-slidable/oil-slidable film-   12 Porous polymer film-   14 Slippery liquid-   20 External liquid

BEST MODE FOR CARRYING OUT THE INVENTION Water-Slidable and Oil-SlidableFilms

FIG. 1 is a schematic drawing of the cross section for thewater-slidable/oil-slidable film of the present invention. As shown inFIG. 1, the water slidable/oil-slidable film 10 of the present inventionhas a porous polymer film 12, in which a fibrous polymer forms theskeleton of a three-dimensional entangled network structure and theempty space has a continuous pore structure, and a slippery liquid 14infused in the pores of the porous polymer film. The external liquid 20on the surface of the water-slidable/oil-slidable film 10 becomes aliquid droplet having a high contact angle and slides down because ofits non-affinity to the slippery liquid 14; thus it is removed and doesnot adhere to the surface.

<Porous Polymer Film>

The polymer that constitutes a porous polymer film is not especiallylimited, in the chemical structure etc., so far as the compound has amolecular weight of 10K or higher. However, from the viewpoint of theantifouling effect against the liquids of various properties(water-sliding/oil-sliding effect), it is preferable to usefluorine-based resins or silicone resins such aspolytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride,polydimethylsiloxane, polymethylphenylsiloxane, and copolymers thereof.In particular, polyvinylidene fluoride or copolymers thereof canpreferably be used.

In the porous polymer film used in the present invention, a fibrouspolymer forms the skeleton of a three-dimensional entangled networkstructure and the empty space has a continuous pore structure. Theporous polymer film can be easily produced under mild conditions in ashort time by the below-described specific method. In simple terms, aporous polymer film of the above structure can be obtained by mixingwith stirring a polymer and a pore-forming agent, at a specific ratio,in a volatile organic solvent, applying the mixture on the substrate anddrying, and then by removing the pore-forming agent with an organicsolvent. Because of such a specific structure of the porous polymerfilm, the slippery liquid infused inside of the pores hardly seeps outor leaks out. Thus, a water-slidable/oil-slidable film that has hightolerance especially to vibration and pressure can be obtained. An epoxyresin array by a photolithography method, porous silicon by etching, andan alumina thin film by a sol-gel method, which are used in theconventional SLIPS, have fine asperity on the surface or non-continuousfine through-holes, and an infused slippery liquid easily seeps out orleaks out. In addition, a porous PTFE sheet formed by the stretchingmethod is a uniaxially-stretched window blind-shaped sheet or abiaxially-stretched cobweb-shaped sheet. Thus, the fibrous polymer isnot entangled in three-dimensional directions and especially in thesheet thickness direction. Therefore, the pore tortuosity factor is lowand the slippery liquid inside the pore seeps out or leaks out byprolonged use or by vibration and pressure; thus the durability is notsatisfactory.

The porous polymer film used in the present invention should have thespecific structure explained above, but it is desirable that thefollowing structural characteristics are additionally satisfied.

The average pore diameter of the porous polymer film is preferably 500to 1000 nm and more preferably 500 to 700 nm. If the pore diameter islarger than the above-described range, slippery liquid cannot beretained, the water-sliding/oil-sliding effect cannot satisfactorily beexhibited, and the durability may be poor. On the other hand, if thepore diameter is smaller than the above-described range, the mechanicalstrength and flexibility of the film itself are not sufficient, and theversatility may be poor. The average pore diameter of the porous polymerfilm can be directly determined from the photographs taken with ascanning electron microscope (SEM), transmission electron microscope(TEM), or atomic force microscope (AFM), or it is calculated by imageprocessing. Alternatively, it can be determined with the use ofcommercial measurement instruments based on the gas adsorption method ormercury intrusion technique.

In the porous polymer film, the average fiber diameter of the fibrouspolymer, which constitutes the skeleton of a network structure, ispreferably 100 to 400 nm and more preferably 300 to 400 nm. If the fiberdiameter is larger than the above-described range, the slippery liquidcannot satisfactorily be retained, and the durability may be poor. Ifthe fiber diameter is smaller than the above-described range, themechanical strength of the film itself may be poor. The average fiberdiameter can be calculated, similarly to the above-described averagepore diameter, from the photographs taken with SEM, TEM, or AFM.

The root-mean-square roughness of the porous polymer film is preferably0.3 to 0.6 μm and more preferably 0.3 to 0.45 μm. In the presentinvention, the root-mean-square roughness is the value [Rq(Rms)]measured according to JIS B0601-2013, and it is defined by thebelow-described equation. If the root-mean-square roughness is largerthan the values in the above-described range, liquid is difficult toslide and the water-sliding/oil-sliding effect may not satisfactorily beexhibited. On the other hand, if the root-mean-square roughness issmaller than the above-described range, the mechanical strength of thefilm itself may be poor. The root-mean-square roughness can normally bemeasured with an atomic force microscope (AFM).

$\begin{matrix}{{Rq} = \sqrt{\frac{1}{l}{\int_{0}^{1}{{Z^{2}(x)}\ {x}}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Rq: root-mean-square roughness, l: reference length, Z(x): height of acontour curve at the position x

The percentage of voids in the porous polymer film is preferably 10 to99% and more preferably 30 to 90%. If the percentage of voids is largerthan the above-described range, slippery liquid cannot be retained, andthe durability may be poor. If the percentage of voids is smaller thanthe above-described range, the amount of infused slippery liquid becomessmall, and the water-sliding/oil-sliding effect may not satisfactorilybe exhibited. The percentage of voids can be calculated, for example,from the measured bulk density and the true density, which ischaracteristic of the polymer.

The thickness of the porous polymer film is not limited in particular;however, it is normally about 1 μm to 5 mm and more preferably 2 μm to 2mm. If the thickness is too small, the amount of infused slippery liquidis small and the durability may be poor. In addition, the strength maynot be sufficient as a self-standing film, which is used by patching onan article, and it may not be usable. On the other hand, if thethickness is too large, the flexibility is poor and it is difficult toapply on an article having a complex structure. In addition, the filmbecomes opaque and may not be usable on an article that needstransparency.

<Slippery Liquid>

The slippery liquid used in the present invention is infused inside thepores of the porous polymer film described above. The slippery liquidneeds to be chemically inert to the porous polymer film, for example, itshould not dissolve the porous polymer. The slippery liquid can beeither hydrophilic or lipophilic; however, it is preferable that theslippery liquid has affinity to the porous polymer film. Here, “hasaffinity” means that the contact angle of the slippery liquid on thesurface of the porous polymer film is less than 90°. If the contactangle of the slippery liquid on the porous polymer film exceeds 90°, itis difficult to infuse the slippery liquid into the pores of the porouspolymer film. Even when the slippery liquid could be infused, it mayseep out or leak out over time. The contact angle between the slipperyliquid and the porous polymer film is more preferably less than 45°.

For example, when an oily liquid is used as the slippery liquid, theantifouling property is mainly exhibited for an aqueous external liquid(water-sliding property). On the other hand, when an aqueous liquid isused as the slippery liquid, the antifouling property is mainlyexhibited for an oily external liquid (oil-sliding property). In orderto exhibit an antifouling property for every kind of liquid, it ispreferable to use fluorine-based oil or silicone oil, namely so-calledwater/oil repellent liquid, as the slippery liquid. Examples includefluorine-based oils such as perfluoropolyether, perfluoroalkylether,perfluorocycloether, perfluoroalkylamine, perfluoroalkylsulfide,perfluoroalkylsulfoxide, perfluoroalkylphosphine, perfluorocarbon,perfluorocarboxylic acid, fluorinated phosphonic acid, fluorinatedsulfonic acid, and fluorinated silane; and silicone oils such asdimethylpolysiloxane, methylphenylpolysiloxane,methylhydrogenpolysiloxane, octamethylcyclotetrasiloxane,decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane,amino-modified silicone oil, polyether-modified silicone oil,carboxy-modified silicone oil, alkyl-modified silicone oil, ammoniumsalt-modified silicone oil, and fluorine-modified silicone oil. Amongthem, perfluoropolyether can most preferably be used.

In addition, it is preferable to select a slippery liquid that has asmall refractive index difference from the porous polymer film. Thus, ahighly transparent water-slidable/oil-slidable film can be obtainedbecause the amount of reflected light at the interface between theporous polymer film and the slippery liquid is small. More specifically,it is preferable that the refractive index difference between the porouspolymer film and the slippery liquid is 0.3 or less, and more preferably0.2 or less. Although it depends upon other conditions such as theporosity (pore diameter, fiber diameter, percentage of voids, etc.) andthe thickness of the porous polymer film, a transparent film whoseaverage transmittance of the light with the wavelength of 400 to 700 nmis 80% or higher can normally be obtained by selecting a combination ofa porous polymer film and a slippery liquid whose refractive indexdifference is small. For instance, high transparency is demanded for thesurface protective plates for solar cells and automobile windshields.For the antifouling purpose of such transparent products, the highlytransparent water-slidable/oil-slidable film can be used.

Production Method

The water-slidable/oil-slidable film of the present invention can beproduced, for example, by carrying out the first step to the fourth stepdescribed below.

<First Step (Coating Solution Preparation Step)>

The step wherein a polymer and a pore-forming agent that does notdissolve the polymer is mixed with stirring in a volatile organicsolvent that can dissolve both the polymer and the pore-forming agent.

<Second Step (Coating Film Formation Step)>

The step wherein a coating film is formed by applying the mixtureobtained in the preceding step on the surface of an article andvaporizing the volatile solvent.

<Third Step (Removal of Pore-Forming Agent/Porous Film Formation Step)>

The step wherein a porous polymer film is formed by allowing the coatingfilm, obtained in the preceding step, to contact with an organic solventthat can dissolve the pore-forming agent and removing the pore-formingagent.

<Fourth Step (Slippery Liquid Infusion Step)>

The step wherein a slippery liquid is infused into the pores of theporous polymer film obtained in the preceding step.

FIG. 2 shows the illustrations of the respective steps as one example ofthe production method of the water-slidable/oil-slidable film of thepresent invention.

<First Step (Coating Solution Preparation Step)>

In the first step, a polymer and a pore-forming agent are mixed withstirring in a volatile organic solvent.

As described in the section of porous polymer films, the polymer usedhere is not especially limited, in the chemical structure etc., so faras the compound has a molecular weight of 10K or higher. However, it ispreferable to use a fluorine-based resin or a silicone resin such aspolytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride,polydimethylsiloxane, polymethylphenylsiloxane, or a copolymer thereof.In particular, polyvinylidene fluoride or a copolymer thereof canpreferably be used. In addition, it is preferable that the polymer issoluble in acetone and insoluble in ethanol.

It is necessary that the pore-forming agent does not dissolve thepolymer but is soluble in the below-described volatile organic solvents.That is, the pore-forming agent and the polymer, which are dissolved inthe volatile organic solvent in the first step, phase-separates afterthe vaporization of the volatile organic solvent in the second step. Inthe third step, when the pore-forming agent is removed, the holeswithout the pore-forming agent become pores and the porous polymer filmis formed. As the pore-forming agent, a low-molecular-weight solventwith the molecular weight of 2000 or less is normally used. For example,ethanol-soluble low-molecular-weight solvents can be used. Among suchlow-molecular-weight solvents, phthalic acid or derivatives thereof canbe preferably used.

The volatile organic solvent preferably has a boiling point of 260° C.or lower and especially preferably 100° C. or lower, and the organicsolvent should dissolve both the polymer and the pore-forming agent.Although it depends upon kinds of polymers and pore-forming agents, theexamples include hydrocarbon solvents such as toluene, benzene, pentane,hexane, heptane, and cyclohexane; halogenated solvents such as methylchloride and methyl bromide: ester solvents such as ethyl acetate; ethersolvents such as diethyl ether, tetrahydrofuran, and ethyl cellosolve;ketone solvents such as acetone, methyl ethyl ketone, and methylisobutyl ketone; and alcohol solvents such as methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol, and t-butanol.

The mixing ratio of the polymer and the pore-forming agent is preferablyin the range of 1:1.5 to 1:5, in the mass ratio, and more preferably inthe range of 1:2 to 1:3. The percentage of the pore-forming agentsignificantly affects the porosity of the obtained polymer porous film,in particular, the percentage of voids, pore diameter, surfaceroughness, etc. If the percentage of the pore-forming agent is toosmall, the amount of infused slippery liquid will be limited, and thewater-sliding/oil-sliding effect cannot be satisfactorily exhibited. Onthe other hand, if the percentage of the pore-forming agent is toolarge, the slippery liquid easily seeps out or leaks out. In addition,the strength and flexibility of the film itself tend to be poor, and itmay not be used as a self-standing water-slidable/oil-slidable film. Theamount of the volatile solvent is not limited in particular; however, itis preferable to adjust the mass concentration ratio to be 20 to 500mass % with respect to the polymer. If the amount of the volatilesolvent is too large, the formation of a coating film takes time. On theother hand, if the amount of the volatile solvent is too small, theapplication by casting or spraying is difficult.

The temperature and time for mixing with stirring are not limited inparticular; however, it is preferable to carry out the step normally at20 to 60° C. for about 10 to 240 minutes. If the mixing with stirring isnot sufficient, the pore-forming agent is non-uniformly distributed inthe mixture; as a result, a porous polymer film having uniform pores maynot be obtained.

<Second Step (Coating Film Formation Step)>

In the subsequent second step, a coating film is formed by applying themixture, obtained in the first step, on the surface of an article andvaporizing the volatile solvent.

An article to be coated can be any object that needs water-slidingoil-sliding properties (antifouling effect). For example, the mixturecan be directly applied on the surface of glass, metal, plastics, etc.Alternatively, a self-standing porous polymer film may be formed byapplying the mixture on a plate of glass or metal, forming a porouspolymer film of a suitable thickness, and peeling it off from the plate.

As the application method of the mixture on the article surface,publicly known coating methods such as a bar-coating method, a spraycoating method, a spin coating method, and a dip coating method can belisted. In addition, the mixture may be printed on the article surfaceby a publicly known printing method. The coating method with the use ofa squeegee is shown in FIG. 2; however, the method is not limited tothis example.

After the application, a coating film consisting of the polymer and thepore-forming agent is formed on the article surface by vaporizing thevolatile solvent. The temperature and time for vaporization depend onthe concentration of the polymer and the pore-forming agent (amount ofvolatile solvent) in the first step; however, the vaporization isnormally conducted at 10 to 40° C. for about 1 to 600 seconds, and morespecifically at ordinary temperature for about 5 seconds.

<Third Step (Removal of Pore-Forming Agent/Porous Film Formation Step)>

In the third step, a porous polymer film is formed by allowing thecoating film obtained in the second step to contact with an organicsolvent that does not dissolve the polymer but can dissolve thepore-forming agent and removing the pore-forming agent.

As the organic solvent, for example, hydrophilic solvents such as water,glycerin, methanol, ethanol, and 2-propanol, or mixed solvents thereofhaving a suitable mixing ratio may be used though it depends upon thekinds of polymers and pore-forming agents. The means for allowing thecontact of the coating film and the organic solvent is not limited inparticular; for example, the coating film is immersed in the organicsolvent for the fixed time as shown in FIG. 2.

In the second step, when the amount of the volatile organic solvent isgradually decreased by vaporization, a phase separation takes placegradually because the polymer and the pore-forming agent are immiscible.When the volatile solvent is completely lost, a coating film wherein thepolymer and the pore-forming agent are coexistent in the state of phaseseparation is formed. In the third step, the pore-forming agent isremoved by immersing this coating film in an organic solvent, the holeswithout the pore-forming agent become pores, and a porous polymer filmis formed. The contact time of the coating film and the organic solventis not limited in particular; however, it is normally immersed in anorganic solvent for about 10 to 600 seconds and more specifically forabout 10 seconds at ordinary temperature.

<Fourth Step (Slippery Liquid Infusion Step)>

In the fourth step, a slippery liquid is infused into the pores of theporous polymer film obtained in the third step.

As described above, the slippery liquid needs to be chemically inert tothe porous polymer film, and it is preferable that the slippery liquidhas affinity to the porous polymer film. The slippery liquid can beeither hydrophilic or lipophilic; however, a fluorine-based oil or asilicone oil having water/oil repellency is preferable, and inparticular, perfluoropolyether can preferably be used.

The means for infusing a slippery liquid is not limited in particular;however, dropwise addition with a dropper or spraying with a sprayer canbe listed as examples. When the affinity of the slippery liquid and theporous polymer film is high, for example, the contact angle of theslippery liquid on the surface of the porous polymer film is less than90° or furthermore less than 45°, the slippery liquid can be rapidlyinfused into the pores of the film only by dropping the slippery liquidon the surface of the porous polymer film.

As explained above, a highly transparent water-slidable/oil-slidablefilm can be obtained by selecting a suitable kind of slippery liquid sothat the refractive index difference is small from the porous polymerfilm. In this case, the porous polymer film normally displays a palewhite color because of the diffuse reflection due to the fine asperityof the surface or that of the interior. However, the porous polymer filminstantly turns transparent by infusing a suitable kind (suitablerefractive index) of slippery liquid. Thus, such a transparent film cansuitably be used for the products requiring transparency.

Thus, the surface of any article can be coated with thewater-slidable/oil-slidable film of the present invention, andwater-sliding oil-sliding properties, namely the antifouling effect canbe provided to the article. Alternatively, a self-standing film can beprepared by forming a water-slidable/oil-slidable film of a suitablethickness, on the surface of a support such as a glass plate, andpeeling off the film from the glass plate. This self-standing film maybe used as the antifouling film by patching on the surface of anyarticle. In particular, a transparent self-standing film can be suitablyused on any product as the antifouling film.

The thickness of a water-slidable/oil-slidable film can be suitablyadjusted, for example, by the amount of coating in the second step. Thethickness is not limited in particular; however, it is normally about 1μm to 2 mm. If the thickness is too small, a satisfactory antifoulingeffect cannot be achieved, and the sufficient strength as theself-standing film may not be obtained. On the other hand, no improvedeffect is observed even when the thickness is larger than necessary. Onthe contrary, the transparency is lost, the flexibility is poor in thecase of a self-standing film, and the application to the intendedarticle may not be possible.

The water-slidable/oil-slidable film of the present invention can beproduced as outlined above. The production does not need ahigh-temperature heat treatment, and all the steps from the first stepto the fourth step can be completed in a very short time. Typically, thefirst step is about 1 hour, the second step is about 1 minute, the thirdstep is about 1 minute, and the fourth step is about 1 minute; thus awater-slidable/oil-slidable film can be produced in a very short time.In addition, the surface of a heat-sensitive article such as athermoplastic resin article can be treated because a high-temperatureheat treatment, for example, at 100° C. or higher is not involved. Thepores of the porous polymer film formed with the pore-forming agent havea skeleton of a three-dimensional entangled network structure of afibrous polymer and the empty space having a continuous pore structure.Therefore, slippery liquid infused into such pores does not easily seepout or leak out by vibration and pressure, and thewater-slidable/oil-slidable film has excellent durability.

Especially suitable articles as the antifouling object for theapplication of the water-slidable/oil-slidable film of the presentinvention are, for example, medical devices, containers, opticalequipment, etc. In many medical devices, blood adhesion becomes thehindrance of operation. For example, the frequent removal of blood thatadheres to an endoscopic instrument is necessary during the operation ofthe device. In the case of containers, the adhesion of the contents suchas food, drinks, and cleaner on the outer surface or the adhesion of theresidues of the contents on the inner surface may become problems. Inthe case of optical equipment, the measurement results may besignificantly affected especially by the liquid adhesion on the lens.The water-slidable/oil-slidable film of the present invention slidesdown various liquids, and their adhesion on the surface can beprevented. The antifouling effect can be exhibited for not only waterand oil but also blood, food, drinks, cleaner, etc.; thus it cansuitably be used for the above articles.

In addition, the water-slidable/oil-slidable film of the presentinvention can be prepared to be a highly transparent film. Therefore,transparent glass products such as window glass and automobilewindshields, which need transparency, can be coated and an antifoulingeffect can be provided. In particular, surface-protective glass platesfor solar cells are installed outside; therefore, various kinds ofmatters such as sand and dust due to rain and wind, fallen leaves, andbird droppings adhere on the surface, and the power generationefficiency may be decreased. On the other hand, the adhesion thereof isprevented by coating with the water-slidable/oil-slidable film of thepresent invention. Even when they temporarily adhere as solid matter,they are washed away with rain water; thus the decrease in the powergeneration efficiency due to adhered dirt can be prevented.

The water-slidable/oil-slidable film of the present invention may bedirectly formed on the article surface of an antifouling object.Alternatively, a pre-formed self-standing water-slidable/oil-slidablefilm may be patched on the object article as described above.

EXAMPLES

Hereinafter, the present invention will be explained in more detail withreference to examples; however, the present invention is not limited bythese examples.

<Materials>

Polymer: poly(vinylidene fluoride-hexafluoropropylene) copolymer(manufactured by Sigma Aldrich Co., PVDF-HFP; Mw: ca. 400000, Mn: ca.130000, HEP/VDF=10 mol %)

Pore-forming agent: di-n-butyl phthalate (manufactured by Kanto ChemicalCo., DBP, 99.5%)

Volatile solvent: acetone (manufactured by Kanto Chemical Co., 99.5%)

Pore-clearing organic solvent: ethanol (manufactured by Kanto ChemicalCo., 99.5%)

Slippery liquid: perfluoropolyether (manufactured by DuPont, PFPE,Krytox 103)

Substrate: glass plate (manufactured by Matsunami Glass Ind., Microslideglass s 122, RI=1.52)

<Preparation of Polymer/Pore-Forming Agent (PVDF-HFP/DBP) Solution>

PVDF-HFP and DBP were added into acetone so that the concentration is 20mass % in total. The various solutions with the PVDF-HFP:DVP mass ratioof 1:0.5, 1:1, 1:2, 1:3, 1:4, and 1:5, respectively, were prepared; theywere stirred at 50° C. for 1 hour and allowed to stand for 1 day ormore.

<Preparation of Porous Polymer Film (PVDF-HFP)>

The polymer/pore-forming agent (PVDF-HFP/DBP) solution was applied onthe surface of a glass plate by a simple wet squeegee method. On theglass plate, two mending tapes with a thickness of 0.058 mm werewrapped, and the PVDF-HFP/DBP solution was applied to the gap with asqueegee. As a result, the volume of the PVDF-HFP/DBP solution on thesurface of the glass plate was 5.8 mm³ per 1.0 cm². The PVDF-HFP/DBPlayer was dried at room temperature for 1 minute or more. Meanwhile,phase separation of PVDF-HFP and DBP took place spontaneously, and itsstructure was fixed by drying. Subsequently, this PVDF-HFP/DBP layer wasimmersed in ethanol for 1 minute or more to extract DBP: then, a porouspolymer film of PVDF-HFP was obtained by blow drying for 10 seconds.

<Production of Water-Slidable/Oil-Slidable Film>

Perfluoropolyether (PFPE) was infused into the PVDF-HFP porous polymerfilm. Initially, the appearance was translucent; however, it becametransparent by the infusion of PFPE. Then, air was blown on the surfaceof the PVDF-HFP film to remove excess PFPE.

<Measurement of Material Properties>

The surface morphology of the PVDF-HFP porous polymer film was examinedwith a field emission scanning electron microscope (FE-SEM, S-4700,manufactured by Hitachi Ltd.). The thickness and surface roughness weredetermined with a laser microscope (VK-9700 Generation II, manufacturedby Keyence Corporation). The sliding angle was measured with a contactangle meter (CA-DT, manufactured by Kyowa Interface Science Co., Ltd.).The transmittance was measured with a UV-VIS spectrophotometer (UV-mini1240, manufactured by Shimadzu Corporation). Photocurrentdensity-voltage curves of the single-crystal standard solar cell(manufactured by CIC) were measured under the conditions of the coatedarea of 2.8 cm² and the irradiation with AM1.5 pseudo-sunlight (1000mWcm⁻²). As the light source, 500 W xenon lamp (UXL-500SX, manufacturedby Ushio Inc.) was used. The mechanical strength and flexibility(extension rate) were determined with a tensile strength tester (EZ-LX,manufactured by Shimadzu Corporation). Test samples for the tensilestrength was 20×60 mm and the thickness was 2 μm.

Surface Morphology of PVDF-HFP Porous Polymer Films

SEM photographs were taken for the porous polymer films prepared byvarying the ratio of polymer/pore-forming agent (PVD-HFP/DBP), and thesurface morphology of the respective films were examined. ThePVD-HFP/DBP ratios of the used porous polymer film were 1:0.5, 1:1, 1:2,and 1:5. The SEM photographs of the respective porous polymer films areshown in FIGS. 3A to 3D.

As shown in FIGS. 3A to 3D, the surface morphology was differentdepending upon the PVD-HFP/DBP ratios. In the ratio of 1:0.5, the filmsurface consisted of flat regions and pores. In the ratios of 1:1, 1:2,and 1:5, a network structure consisting of fibers and pores was formed.If the ratio of 1:0.5 and the ratio of 1:1 are compared, the poredensity increases with an increase in the amount of DBP, and the flatregions decrease. Therefore, in the ratio of 1:1, the film surface isfibrous rather than flat. In the ratio of 1:2, the pore density furtherincreases than the ratio of 1:1, and the fiber diameter becomes small.If the ratio of 1:2 and the ratio of 1:5 are compared, the size ofindividual pores increases though the fiber diameter becomes smaller.This is considered to be due to interconnected pores, which are causedby the increase of pore density.

The measurement results of the pore size and fiber diameter for variousporous polymer films with different PVD-HFP/DBP ratios are shown inTable 1 and FIG. 4.

TABLE 1 PVD-HFP/DBP ratio 1:0.5 1:1 1:2 1:5 Fiber diameter 650 460 330250 (nm) Pore size 660 460 570 850 (nm)

As shown in Table 1 and FIG. 4, the fiber diameter had a decreasingtrend with the increase of the proportion of DBP. On the other hand, thepore size was observed to increase with the increase of the amount ofDBP except for the ratio of 1:0.5. The pore size for 1:0.5 was largerthan that of 1:1 because the pore has an ample-shaped structure in theratio of 1:1. That is, the pore has a small opening and a larger innerspace; therefore, the pore size looks smaller. Such an ample-shapedstructure is considered to be formed because DBP with a smaller specificgravity is immobilized during the rise to the surface when acetone isvaporized and the phase separation of PVDF-HFP and DBP takes place inthe process of forming a coating film.

Measurement results of the surface roughness (root-mean-squareroughness: Rms) for various porous polymer films of differentPVD-HFP/DBP ratios are shown in Table 2 and FIG. 5.

TABLE 2 PVD-HFP/DBP ratio 1:0.5 1:1 1:2 1:3 1:4 1:5 Surface Roughness0.25 0.28 0.4 0.46 0.48 0.49 RMS (μm)

As shown in Table 2 and FIG. 5, the surface roughness was observed toincrease with the increase of the proportion of DBP. The difference inthe surface roughness was the largest between the ratios of 1:1 and 1:2,and the difference was not so large from the ratio of 1:2 to the ratioof 1:5.

The measurement results of the thickness for various porous polymerfilms with different PVD-HFP/DBP ratios are shown in Table 3 and FIG. 6.

TABLE 3 PVD-HFP/DBP ratio 1:0.5 1:1 1:2 1:3 1:4 1:5 Thickness (μm) 2.12.1 2.1 1.9 1.7 1.6

As shown in Table 3 and FIG. 6, the thickness of a porous polymer filmwas almost the same from the ratio of 1:0.5 to 1:3, thinner in the ratioof 1:4, and much thinner in the ratio 1:5. In the range from the ratioof 1:0.5 to 1:3, the increase of the proportion of DBP affects theincrease in the porosity (percentage of voids). On the other hand, ifthe proportion of DBP exceeds 1:4, the thickness is considered todecrease because of excessive DBP. Therefore, a porous polymer filmwhose PVD-HFP/DBP ratio exceeds 1:4 is considered to be more fragile.The mechanical strength and flexibility of the film will be describedlater.

Sliding Angle of Water-Slidable/Oil-Slidable Film

The measurement results of the sliding angles of water and oil (oleicacid) on the water-slidable/oil-slidable films prepared from variousporous polymer films with different PVD-HFP/DBP ratios are shown inTable 4 and FIG. 7. As the slippery liquid, perfluoropolyether (PFPE)was used.

TABLE 4 PVD-HFP/DBP ratio 1:0.5 1:1 1:2 1:5 Water-sliding angle 27 25 66 (°) Oleic acid-sliding angle — — 4 4 (°)

As shown in Table 4 and FIG. 7, the sliding angles of both water andoleic acid were small on the films of the ratios of 1:2 and 1:5. On theother hand, the sliding angles on the films of the ratios of 1:0.5 and1:1 were large, and the liquid adhered on the film surface.

FIG. 8 shows explanatory illustrations of liquid adhesion on the surfaceof the PVDF-HFP porous (PFPE-infused) film. As shown in FIGS. 3A and 3B,flat regions were present on the film surface in the cases of 1:0.5 and1:1. In addition, the surface roughness was also smaller compared withthat of the film of the ratio of 1:2 or 1:5. Therefore, the films of theratios of 1:0.5 and 1:1 do not have a structure suitable for theretention of slippery liquid. That is, the slippery liquid cannot beretained on the flat region. As shown in the top section of FIG. 8,liquid droplets are trapped on the exposed flat region and adherethereto. On the other hand, the films of the ratios of 1:2 and 1:5 havehardly any flat regions as shown in the bottom section of FIG. 8; thusboth water and oleic acid display very small sliding angles. The filmsof the ratios of 1:2 and 1:5 also display small sliding angles 3.4° and3.6°, respectively, to hexane having a smaller surface energy. Thus,these water-slidable/oil-slidable films slide down and remove variouskinds of liquids; as a result, the dirt due to adhesion thereof may beprevented.

Transparency of Water-Slidable/Oil-Slidable Films

The measurement results of the transmittance in the visible lightregion, for various PVDF-HFP films before and after the infusion of theslippery liquid (PFPE), are shown in FIG. 9. In FIG. 9, solid line A isafter the infusion of PFPE, and dotted line B is before the infusion ofPFPE. In addition, the measurement results for the transmittance oflight with the wavelength of 600 nm are shown in Table 5 and FIG. 10.

TABLE 5 PVD-HFP/DBP ratio 1:0.5 1:1 1:2 1:5 Glass Transmittance BeforePFPE 72.7 62.1 33.9 35.9 92.0 of 600 nm light Infusion (%) After PFPE88.8 87.0 87.4 88.1 92.0 Infusion

As shown in FIG. 9, the transmittance in the visible light region wasless than 80%, for all the PVDF-HFP films, before the infusion of PFPE.However, the transmittance after the infusion of PFPE was roughly about80%. As shown in Table 5 and FIG. 10, the transmittance of light withthe wavelength of 600 nm was about 88% after the infusion of PFPE. Therefractive index (RI) of PVDF-HFP film is 1.40, and PVDF-HPF (RI=1.40)and air (RI=1.00) are present, before the infusion of PFPE, in the lightpath inside the film. On the other hand, PVDF-HPF (RI=1.40) and PFPE(RI=1.29) are present inside the film after the infusion of PFPE and therefractive index difference is small; therefore, the reflection at theinterface is also very small. The light reflectance between the twomaterials were calculated to be 2.8% for PVDF-HFP/air and 0.17% forPVDF-HFP/PFPE. Accordingly scattered reflection is generated at theinterface between the PVDF-HPF fibers and air, before the infusion ofPFPE, and resulting in low transparency. On the other hand, lightreflection at the interface between PVDF-HFP and PFPE becomes smallafter the infusion of PFPE, resulting in high transparency. The lighttransmittance of the PVDF-HPF film after the infusion of PFPE is onlyabout 5% different from that of the uncoated glass plate, and thetransparency was confirmed to be very high.

FIG. 11 shows a photograph of glasses in which a PVDF-HFP porous(PFPE-infused) film was formed on the surface of a rounded lens by acast method. The left lens is uncoated, and the right lens is coatedwith the PVDF-HFP porous (PFPE-infused) film. As shown in FIG. 11, thetransparency of the right lens coated with the PVDF-HFP porous(PFPE-infused) film is comparable to that of the uncoated left lens, andit is satisfactorily usable as glasses. In FIG. 11, water droplets onthe surface of the right lens are sliding; the arrows in the figureindicate the sliding directions of water droplets.

A bare solar cell, a solar cell covered a glass plate, solar cellscovered with the respective glass plates coated with a PVDF-HFP film(before PFPE-infusion) and a PVDF-HFP film (after PFPE infusion) wereprepared, and the photocurrent density (Jsc)-voltage (Voc) curves forthe respective solar cells were measured; and the results are shown inFIG. 12. The film of the PVD-HFP/DBP ratio of 1:2 was used. In addition,the fill factor (FF) and the photoelectric conversion efficiency η weremeasured for the respective solar cells. The results are shown in Table6.

TABLE 6 Voc Jsc η [V] [mA/cm2] FF [%] Bare solar cell 1.073 13.722 0.70110.323 Glass covered cell 1.073 13.093 0.705 9.898 PVDF-HFP Film 1.0589.337 0.684 6.751 (Before PFPE Infusion) PVDF-HFP Film 1.066 12.9340.677 9.333 (After PFPE Infusion)

The results shown in FIG. 12 and Table 6 are approximately in agreementwith the results of transmittance measurements shown in FIGS. 9 and 10.As shown in Table 6, the cell characteristics, in particular thephotoelectric conversion efficiency η decreased significantly in thesolar cell prepared with the use of a PVDF-HFP film before the infusionof PFPE compared with that for the bare solar cell or the glass-coveredsolar cell. However, in the solar cell prepared with the use of aPVDF-HFP film after the infusion of PFPE, the decreases in various cellcharacteristics were suppressed. The tests were performed with the useof PVDF-HFP films coated on the glass plates; therefore, a decrease inthe photoelectric conversion efficiency η due to the coating of thePVDF-HFP film after the infusion of PFPE is virtually 0.565% (differencefrom the glass-covered solar cell). From these results, the PVDF-HFPfilm after the infusion of PFPE is considered to be useful as theantifouling film for solar cells.

Mechanical Strength and Flexibility of Water-Slidable/Oil-Slidable Films

An adhesive tape was pasted at the edge of the PVDF-HFP film that wasprepared on a glass plate. The tape was peeled off and the PVDF-HFP filmwas simultaneously separated from the glass plate. The tensile strengthof the obtained self-standing film of PVDF-HFP (PFPE-infused) wasmeasured and the results are shown in Table 7 and FIG. 13, and theextension rate was also measured and the results are shown in Table 8and FIG. 14.

TABLE 7 PVD-HFP/DBP ratio 1:0.5 1:1 1:2 1:5 Tensile strength 0.80 0.370.22 — (N)

TABLE 8 PVD-HFP/DBP ratio 1:0.5 1:1 1:2 1:5 Extension rate 334.0 344.3168.8 — (%)

As shown in Table 7 and FIG. 13, the tensile strength decreased with theincrease of the proportion of DBP; a self-standing film could not beobtained in the ratio of 1:5. This is because the density of thePVDF-HFP skeleton decreases inversely with the increase of theproportion of DBP, as is clear from FIGS. 3A to 3D. The tensile strengthof the film with the proportion of DBP of 1:2 was the smallest and itwas 0.22 N. As shown in Table 8 and FIG. 14, the extension rate of theself-standing film of PVDF-HFP (PFPE-infused) was 168.8% or higher andexcellent flexibility was displayed.

FIG. 15 shows a photograph of the self-standing film of PVDF-HFP(PFPE-infused) prepared with the proportion of DBP of 1:2 in theabove-described test. As shown in FIG. 15, the self-standing filmobtained by peeling off from the glass plate has high transparency, andit is also usable as a self-standing film. Therefore, the film can beused, for example, by pasting on any article as a disposable antifoulingfilm.

Durability of Water-Slidable/Oil-Slidable Films

PFPE was infused into a PVDF-HFP film formed on the surface of a glassplate, the film was rotated for 1 minute at various spin speeds, andthen the water sliding angle was measured. The results are shown inTable 9 and FIG. 16.

TABLE 9 Spin speed (rpm) 0 1000 2000 4000 6000 Water-sliding angle 5.55.5 5.5 5.6 5.8 (°)

As shown in Table 9 and FIG. 16, the water-sliding effect (water slidingangle) was hardly affected by the rotation of the PVDF-HFP(PFPE-infused) film. From the results, it was clarified that PFPE doesnot seep out or leak out, from the PVDF-HFP porous film, by rotation andthat the water-slidable/oil-slidable film has excellent durability.

Similarly to the above-described test, abrasion was applied to thePVDF-HFP (PFPE-infused) film under a loading condition of 80 g/cm² forthe defined time, and the water sliding angle was measured; the resultsare shown in Table 10 and FIG. 17.

TABLE 10 Abrasion time (sec) 0 100 500 1000 Water-sliding angle 5.5 5.55.8 5.7 (°)

As shown in Table 10 and FIG. 17, the measurement results of the watersliding angle hardly changed after the application of abrasion to thePVDF-HFP (PFPE-infused) film. Thus, it was confirmed that PFPE does notseep out or leak out from the PVDF-HFP porous film. Similarly to theabove rotation test, the excellent durability is considered to be due tothe internal structure of the PVDF-HFP porous film. That is, fibrouspolymer forms a skeleton, which has a three-dimensional entanglednetwork structure, inside the PVDF-HFP porous film, and PFPE is infusedinside the continuous pores of the empty space. Therefore, PFPE insidethe pores does not easily seep out or leak out by rotation or abrasion.As a result, a water-slidable/oil-slidable film with excellentdurability can be obtained.

Antifouling Property Against Various Liquids

To the PVDF-HFP (PFPE-infused) film, of PVDF-HFP/DBP ratio of 1:2,prepared on the surface of a glass plate, various liquids with differentproperties were dropped, and the antifouling property against theliquids were evaluated. FIGS. 18A to 18D show their photographs. Theused liquids are as follows, A: blood, B: high-viscosity drink (sweetbean soup), C: food oil, D: cleaner.

As shown in FIGS. 18A to 18D, the PVDF-HFP (PFPE-infused) film displayshigh contact angles for all the liquids, and liquid droplets immediatelyslid down when the glass plate is slanted (FIGS. 18A to 18D showphotographs in which liquid droplets are sliding). Thus, an excellentantifouling effect can be provided, against various liquids havingdifferent properties, by the PVDF-HFP (PFPE-infused) film.

What is claimed is:
 1. A water-slidable/oil-slidable film comprising: aporous polymer film having a three-dimensional entangled networkstructure of a fibrous polymer and a continuous pore structure as theempty space of the network structure, and a slippery liquid infused inthe pores of the porous polymer film.
 2. The water-slidable/oil-slidablefilm of the claim 1, wherein an average pore diameter of the porouspolymer film is 500 to 1000 nm.
 3. The water-slidable/oil-slidable filmof the claim 1, wherein an average fiber diameter of the porous polymerfilm is 100 to 400 nm.
 4. The water-slidable/oil-slidable film of theclaim 1, wherein root-mean-square roughness of the porous polymer filmis 0.3 to 0.6 μm.
 5. The water-slidable/oil-slidable film of the claim1, wherein the porous polymer film is made of a fluorine-based resin orsilicone resin.
 6. The water-slidable/oil-slidable film of the claim 5,wherein the porous polymer film is made of polyvinylidene fluoride orcopolymer thereof.
 7. The water-slidable/oil-slidable film of the claim1, wherein the slippery liquid has affinity to the porous polymer film.8. The water-slidable/oil-slidable film of the claim 1, wherein theslippery liquid is a fluorine-based oil or silicone oil.
 9. Thewater-slidable/oil-slidable film of the claim 8, wherein the slipperyliquid is perfluoropolyether.
 10. The water-slidable/oil-slidable filmof the claim 1, wherein the refractive index difference between theporous polymer film and the slippery liquid is 0.3 or less.
 11. Thewater-slidable/oil-slidable film of the claim 1, wherein an averagetransmittance of the light with the wavelength of 400 to 700 nm is 80%or higher.
 12. A production method of water-slidable/oil-slidable filmcomprising: a step of mixing with stirring a polymer and a pore-formingagent that does not dissolve the polymer and a volatile organic solventthat can dissolve both the polymer and the pore-forming agent, a step offorming a coating film by applying the mixture obtained in the precedingstep on the surface of an article, and vaporizing the volatile organicsolvent, a step of forming a porous polymer film by contacting thecoating film obtained in the preceding step with an organic solventallowing that can dissolve the pore-forming agent without dissolving thepolymer, to remove the pore-forming agent from the coating film, a stepof infusing a slippery liquid inside the pores of the porous polymerfilm obtained in the preceding step.
 13. The production method ofwater-slidable/oil-slidable film of the claim 12, wherein a mixing ratio(mass ratio) of the polymer to the pore-forming agent is 1:1.5 to 1:5.14. The production method of water-slidable/oil-slidable film of theclaim 12, wherein the polymer is a fluorine-based resin or siliconeresin.
 15. The production method of water-slidable/oil-slidable film ofthe claim 12, wherein the polymer is polyvinylidene fluoride orcopolymers thereof.
 16. The production method ofwater-slidable/oil-slidable film of the claim 12, wherein the polymer issoluble in acetone and insoluble in ethanol.
 17. The production methodof water-slidable/oil-slidable film of the claim 12, wherein thepore-forming agent is an ethanol-soluble low-molecular-weight solvent.18. The production method of water-slidable/oil-slidable film of theclaim 12, wherein the pore-forming agent is phthalic acid or derivativesthereof.
 19. The production method of water-slidable/oil-slidable filmof the claim 12, wherein the volatile organic solvent is an organicsolvent with a boiling point of 100° C. or lower.
 20. The productionmethod of water-slidable/oil-slidable film of the claim 12, wherein thevolatile organic solvent is acetone.
 21. The production method ofwater-slidable/oil-slidable film of the claim 12, wherein the organicsolvent that can dissolve the pore-forming agent without dissolving thepolymer is ethanol.
 22. The production method ofwater-slidable/oil-slidable film of the claim 12, wherein the slipperyliquid is a fluorine-based oil or silicone oil.
 23. The productionmethod of water-slidable/oil-slidable film of the claim 22, wherein theslippery liquid is perfluoropolyether.
 24. An article having the surfacecoated with the water-slidable/oil-slidable film of the claim 1.